it can cause severe neurologic signs such as the animal falling, circling, or being unable to rise. The parasite lives in the brains of deer and lays many eggs into the blood stream, which then hatch. They are then excreted by the deer where they are picked up by various snails and slugs in whose systems the worm develops even more. The gastropod is then eaten by another animal such as another deer, or another “aberrant host,” such as a camelid, where it migrates to the nervous system and causes disease. So when we think about controlling this parasite, we can intervene at several different stages.
1. Prevent overlap between deer and camelids
2. Prevent ingestion of infected gastropods by camelids
3. Kill the worm between initial infection and onset of clinical signs
The best prevention strategy is a combination of all of these, if possible. Start with decreasing contact with white tail deer. This is best achieved with an 8 foot fence surrounding all areas where camelids are kept. This can be expensive; however, it is one of the best ways to prevent deer from excreting larva of P.Tenuis where they can be eaten by camelids. The second method is to prevent ingestion of the snails and slugs. If an appropriate fence has been put up, putting a 5 foot gravel strip along the fence line discourages and almost completely prevents gastropods from crossing that line. Think of it as a slug fence! Whether or not a slug fence can be made, poultry can be kept to decrease the number of slugs and snails that are on pasture. Appropriate choices to accomplish this would include: chickens, geese, ducks, or Guinea hens. The last resort would be to kill the worm once it is already infecting the camelids. This is typically done by giving a monthly ivermectin shot to all camelids.
Giving monthly shots is the most common method because it is typically the cheapest and easiest method. However, interrupting transmission by preventing access by deer and slugs is just as effective without monthly shots to all the camelids.
A potential problem with this last approach arises because camelids get another parasite called the barber pole worm, which is an intestinal parasite that can cause fatal anemia if it is uncontrolled. When monthly shots of ivermectin are given, resistance will develop against this anthelmintic in the barber pole worm. There are still two other classes of anthelmintic that can be effective against the barber pole worm, however this is essentially removing one of three tools from the anti-parasite tool box and will increase the chance that the barber pole worm can no longer be controlled. Therefore, the best recommendation is to build a deer fence with a slug fence and potentially keep poultry, as well, with access to the pasture. If monthly shots are given, only give them from spring thaw until the first freeze, since the gastropods will go into a hibernation type state during the winter. As always, please contact us with any questions or help with developing the best plan for you and your animals!